1. Field of the Invention
The present invention relates to an illumination device adapted for a video camera, a film-using camera, a digital camera or the like to be used for photo-taking, and to a photographing apparatus having the illumination device.
2. Description of Related Art
An illumination device used with a photographing apparatus such as a camera or the like for illuminating an object of shooting is composed of a light source (a flash discharge tube) and optical members such as a reflection mirror for guiding a light flux emitted from the light source toward the object, a Fresnel lens, etc.
In respect of such an illumination device, various contrivances have heretofore been made for efficiently collecting a light flux emitted from the light source in the various directions within a necessary angle range of illumination.
Particularly, various illumination devices have recently come to be arranged to enhance light-collecting efficiency and to permit reduction in size by using the total reflection of a prism light guide instead of using the Fresnel lens which has conventionally been disposed in front of the light source.
Meanwhile, illumination devices of the kind having a fixed illumination range have come to present a problem in that a large loss of energy is caused by the inclusion of an unnecessary illumination range in the event of photo-taking at a telephoto position for a narrow illumination range, because the photographing apparatuses have come to be popularly arranged to have a high rate of magnification for zooming. To solve this problem, various illumination devices have been developed to have a variable illumination angle which can be varied according to the range of photo-taking.
For example, an illumination device disclosed in Japanese Laid-Open Patent Application No. HEI 4-138439 is arranged to vary the illumination range. In this case, a total-reflection surface is switched between a reflecting state and a transmitting state from one over to the other by varying the relative positions of an optical prism and a light source.
In another illumination device disclosed in Japanese Laid-Open Patent Application No. HEI 8-262538, an optical prism is divided into upper and lower prisms. The illumination range is changed from one range over to another by rotating the upper and lower optical prisms.
Reduction in weight and size of photographing apparatuses such as cameras have recently furthered. The photo-taking lenses of these apparatuses are meanwhile trending to have a higher rate of zoom magnification. Generally, the reduction in size of the photographing apparatus and the increase in the rate of zoom magnification tend to cause the photo-taking lens to become darker, i.e., to have a larger F-number. Photo-taking with such a dark photo-taking lens without using any auxiliary light source tends to result in a failure, i.e., a blurred picture, caused by image shakes as a shutter speed is set to a slow speed under an automatic exposure control.
To solve this problem, a photographing apparatus, such as a camera, is generally provided with a built-in illumination device (hereinafter referred to as a flash device) which is to be used as an auxiliary light source. In the above-stated background situation, the frequency of use of an auxiliary illumination device is trending to increase to a great degree as compared with the past situation. In addition to that, an amount of light emission per shot is also trending to increase.
Such being the background situation, the illumination device disclosed in Japanese Laid-Open Patent Application No. HEI 4-138439 is arranged to include a light-collecting optical system wherein upper and lower two surfaces are arranged in front of a flash device to cause light fluxes emitted mainly sideway from the light source to enter an optical member and then to be collected in a predetermined direction by total reflection, a surface is arranged in front of the light source to have a positive refractive power so as to collect light, and, after light fluxes are collected respectively by these surfaces, the light fluxes are allowed to exit from one and the same exit surface toward the object of shooting. The range of illumination by the illumination device is arranged to be variable with the reflecting and transmitting actions of a total-reflection surface switched from one over to the other by varying the relative positions of an optical prism and the light source in the light-collecting optical system.
However, in order to accurately vary the angle of illumination according to the above-mentioned method, the surface shape for switching between the total reflection and the transmission is restricted too much for sufficiently allowing latitude in designing the shape of the optical prism. A light quantity loss takes place in a transmitted component at the time of entrance and exit. Further, the size of an effective light-emitting part of the light source greatly contributes to the distribution of luminous intensity. These factors make design work difficult.
The illumination device disclosed in Japanese Laid-Open Patent Application No. HEI 8-262538 is arranged to divide an optical prism into upper and lower prisms and to change the illumination range from one range over to another by rotating the upper and lower optical prisms. According to such an arrangement, however, it is basically only the illuminating direction of the totally-reflected light component that is shifted on the whole, while the luminance intensity distribution characteristic of the illumination device is left unvaried. It is, therefore, hardly possible to obtain a uniform luminance intensity distribution at each of various zoom points.
In the above-stated case, a maximum light-collecting state is obtained when the three areas including the upper, lower and middle areas are overlapped. Then, the range of illumination is expanded by gradually shifting the upper and lower luminance intensity distributions outward by causing the optical prism to rotate. However, while the shift is in process, some in continuous points arise at the overlapping parts among the upper, middle and lower luminance intensity distributions to prevent a uniform distribution within the whole illumination range. The above-mentioned arrangement thus sometimes gives a partly uneven illuminance.
Further, the above-stated illumination device has necessitated use of three optical prism members including the upper, middle and lower prism members and also some parts to be arranged for moving two optical prisms in synchronism with each other. The arrangement of mechanical parts, therefore, tends to become complex.
It is an object of the invention to provide an illumination device, or a photographing apparatus having the illumination device, wherein an illumination optical system is formed in a configuration which is more compact as a whole than the conventional illumination optical system and yet is arranged to be capable of varying the angle of illumination.
It is another object of the invention to provide an illumination device, or a photographing apparatus having the illumination device, arranged to have a uniform luminous intensity distribution characteristic at every zoom point and to minimize the amount of movement required for varying the angle of illumination.
It is a further object of the invention to provide an illumination device arranged to be extremely small and thin in size and light in weight and to have a variable illumination angle.
It is a still further object of the invention to provide an illumination device, or a photographing apparatus having the illumination device, arranged to be capable of utilizing energy obtained from a light source at a high rate of efficiency, obtaining a uniform luminous intensity distribution characteristic at every zoom point and to be highly suited for a still camera, a video camera, a digital camera or the like.
To attain the above objects, in accordance with an aspect of the invention, there is provided an illumination device, comprising a light source, a first optical member having a total-reflection surface for totally reflecting at least a part of incident light, light emitted from the light source being made incident on the first optical member, and a second optical member, light having exited from the first optical member being made incident on the second optical member, wherein the illumination device varies a state of illumination light by varying a positional relationship between the first optical member and the second optical member.
Further, in accordance with another aspect of the invention, there is provided a photographing apparatus, comprising a photographic optical system, and the above illumination device, wherein the photographing apparatus varies a state of illumination light emitted from the illumination device, according to a state of the photographic optical system.
The above and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.